The present invention generally relates to switching systems, and more particularly to a switching system which is connected via a link to a radio base station of a mobile communication system that carries out switching of channels in service, and processes calls generated in the mobile communication system.
The Code Division Multiple Access (CDMA) was frequently used in communication for military purposes because the CDMA has a superior secrecy and is strong against interference. However, by positively utilizing the strong anti-interference characteristic of the CDMA, it is possible in general to improve the utilization efficiency of radio frequencies. In addition, since techniques for realizing a transmission power control with a high accuracy and an improved response have been established recently, the CDMA is now being applied to mobile communication systems in which mobile stations scattered in radio zones move while maintaining a service state and the switching of the channels in service, that is, handover of the channels, is carried out.
In the mobile communication system applied with the CDMA, the levels of the received waves reaching the base stations of the adjacent radio zones from the mobile station which is the subject of the handover are appropriately varied under the transmission power control described above. For this reason, unlike the mobile communication systems applied with the Time Division Multiple Access (TDMA) or the Frequency Division Multiple Access (FDMA), the radio zone to which the handover is to be made cannot be determined to a single radio zone depending on the levels of the received waves.
Accordingly, in the mobile communication system applied with the CDMA uses an Asynchronous Transfer Mode (ATM) switching system which can smoothly and dynamically switch the radio zone to the radio zone handed over with the call. The ATM switching system and each radio base station are connected via a link adapted to the ATM.
However, in the mobile communication system applied with the CDMA, it was difficult to use a conventional ATM switching system without greatly modifying the construction of the conventional ATM switching system.
In addition, a delay in updating identification information related to the handover causes considerable deterioration of the speech quality, and it was particularly difficult to apply the conventional ATM switching system to a call of a telephone system in the mobile communication system.